Detecting proximity or approach of a user's hand (or other body part) permits an electronic device to automatically change from one state to another based upon that approach or proximity. One important application for this is in conjunction with power management. For example, a device can be configured to have “sleep” and “awake” states. During a sleep state, which can correspond to periods of device non-use, various components and functions can be turned off so as to minimize power consumption. Non-use of a device often corresponds to periods when a user is not holding or near the device. If the device can detect the user's presence and/or contact, the device can be configured to automatically awaken (or remain awake) when the user is present and to sleep when the user is not present. In some applications, changes in hand or body part proximity may occur infrequently. Detecting and interpreting a change in proximity conditions could similarly facilitate re-evaluation of a power (or other) state.
Wireless computer input devices such as a computer mouse are but one example of a device in which power consumption is a concern. Typically, a computer mouse includes motion detection components, internal circuitry for converting the detected motion into data for transmission to a computer, and one or more buttons, scroll wheels, etc. In the case of a wireless mouse, the mouse further contains circuitry for wireless (typically RF) communication with a receiver that is connected to a computer. All of these mouse components require power to function, and the mouse consumes more power if these components are used more frequently. At the same time, wireless computer input devices have a limited battery power supply. Nevertheless, because of the added convenience offered by such devices, wireless computer mice and other peripherals are becoming increasingly popular with computer users.
Power consumption can be especially critical in optically tracking wireless mice. Unlike earlier designs in which motion is detected by a pair of encoder wheels that are rotated by a rolling ball, optical mice do not require moving parts to detect motion (other than the mouse itself relative to some surface). Instead, an optical mouse takes a series of images of the surface over which it moves, and then compares the images to determine the direction and magnitude of motion. Examples of such optical input devices and related signal processing are described in, e.g., U.S. Pat. No. 6,303,924 (titled “Image Sensing Operator Input Device”) and U.S. Pat. No. 6,172,354 (titled “Operator Input Device”). As described in those patents, an array of photo-sensitive elements generates an image of a desktop (or other surface) portion when light from an associated illumination source reflects from the desktop or other surface. Although optical input devices offer numerous advantages over devices that mechanically encode motion, optical devices often consume more power than mechanical designs. It is therefore advantageous if a wireless optical mouse can sleep or otherwise enter a reduced power mode when not in use. Unlike some wireless computer mice employing mechanical encoder wheels, however, periodically testing for mouse motion as a method of waking a sleeping optical mouse is problematic. Instead of sampling motion detector elements for an indication of recent movement, the proximity of a user's hand can be used as an indicator that the mouse must wake up.
Various types of user proximity detectors are known and used in power management systems and other applications. For example, Mese et al. U.S. Pat. No. 5,396,443 discloses power saving control arrangements for an information processing apparatus. More specifically, the Mese et al. patent describes various systems for (1) detecting the approach (or contact) of a user associated medium to (or with) the apparatus; (2) placing a controlled object of the apparatus in a non-power saving state when such contact or approach is detected; and (3) placing the controlled object in a power saving state when the presence of the user associated medium (i.e., a stylus pen or part of a user's body) is not detected for a predetermined period of time. The '443 patent describes various types of approach/contact sensors. Among these, various “tablet” type sensor systems are described, including electromagnetic, capacitance, and electrostatic coupling tablets. In one embodiment, a contact or approach detecting tablet, and a flat display panel, may be integrally formed with a housing of the information processing apparatus.
Sellers U.S. Pat. No. 5,669,004 discloses a system for reducing power usage in a personal computer. More specifically, a power control circuit is disclosed for powering down portions of a personal computer in response to user inactivity, and for delivering full power to these portions once user activity is detected via one or more sensors. In the primary embodiment that is disclosed, the sensor is a piezoelectric sensor fitted into a keyboard. Sellers discloses that sensors may be positioned at other locations on the computer (a monitor, mouse, trackball, touch pad or touch screen) and that various other kinds of sensors (capacity, stress, temperature, light) could be used instead of piezoelectric sensors.
Commonly owned Casebolt et al. U.S. patent application Ser. No. 09/948,099, filed Sep. 7, 2001 and published under No. 20020035701 on Mar. 21, 2002, discloses capacitive sensing and data input device power management systems and methods. In the disclosed embodiments, capacitive proximity sensing is carried out by detecting a relative change in the capacitance of a “scoop” capacitor formed by a conductor and surrounding ground plane. The conductor may be a plate provided in the form of an adhesive label printed with conductive ink. Charge is transferred between the scoop capacitor and a relatively large “bucket” capacitor, and a voltage of the bucket capacitor is applied to an input threshold switch. A state transition from low to high (or high to low) of the input threshold is detected, and a value indicative of the number of cycles of charge transfer required to reach the state transition is determined. The presence or absence of an object or body portion in close proximity to or in contact with a device can be determined by comparing the value with a predetermined threshold. The predetermined threshold can be adjusted to take into account environmentally induced changes in capacitance of the scoop capacitor.
Junod et al. U.S. patent application Ser. No. 10/124,892, filed Apr. 17, 2002 and published under No. 20020126094, discloses a computer input device with a capacitive antenna. Electrodes are disposed within and/or on the device housing. Proximity of a user's hand and/or direct contact by a hand causes changes in capacitance, which are then used to awaken the input device from a sleep mode. The capacitive electrodes are also used as a capacitive antenna for data transmission by the input device. Although the '892 application refers to use of an inductive antenna and inductive detection circuit, no description of such a system is provided.